Tutorial 1 - Blink an LED

Learn how to make an LED blink using an Arduino. This is the classic first project that introduces you to digital output and timing with delay().

Circuit Diagram

💡Tip: Pin 13 has a built-in LED too — great for quick testing without any components, and it'll still blink!

What You'll Need

Arduino Uno x 1
Breadboard x 1
LED x 1
220Ω Resistor x 1
Jumper wires x 2
USB Cable x 1
Arduino IDE installed

Instructions

Connect the long leg of the LED (anode) to digital pin 13 on the Arduino.
Connect the short leg (cathode) to one side of a 220Ω resistor.
Connect the other side of the resistor to GND on the Arduino.
Plug your Arduino into your computer using a USB cable.
Open the Arduino IDE, and paste in the code below.
Under Tools, select your board type and COM port.
Click Upload. Your LED should start blinking!

The Code


void setup() {
pinMode(13, OUTPUT); // Set pin 13 as an output
}

void loop() {
digitalWrite(13, HIGH); // Turn LED on
delay(1000);            // Wait 1 second
digitalWrite(13, LOW);  // Turn LED off
delay(1000);            // Wait 1 second
}

Schematic Diagram

Schematic diagrams show how current flows and how components connect logically — not just physically.

Common Mistakes to Watch For

Pin number in code doesn’t match your wiring — Double-check the LED is connected to the same pin you use in pinMode() and digitalWrite().
Placing the jumper wire on the wrong side of the resistor — The LED won’t light up if current doesn’t flow through the resistor properly. Make sure the resistor bridges the correct rows.
Forgetting to set the pin as OUTPUT — If you skip pinMode(13, OUTPUT); , the LED won’t light up.
Using the wrong resistor value — too high = dim, too low = risky burn.